A series of small earthquakes have rocked the underground of southern Albany County, including Altamont and the Hilltowns, in the past four months, leaving residents to wonder about the cause, and the possibility for bigger quakes in the future.

The United States Geological Survey recorded a magnitude three earthquake in Berne, at 8:53 p.m., on Sunday, May 17, followed by a smaller earthquake at 3:21 a.m. on Monday. The two tremors were only the most recent in a succession of 15 small earthquakes that have occurred in the region since February.

According to information from the USGS, the earthquake on Sunday was centered around the intersection of county routes 1 and 3, at a depth of about 5.6 miles underground; the aftershock, on Monday morning, was centered in the same area, at a shallower depth of 3.7 miles.

The largest earthquakes in the region have been a magnitude of three, which is just large enough to be felt indoors. A larger quake can’t be ruled out in the future, but isn’t probable, according to John Ebel, a professor of geophysics at Boston College and director of the Weston Observatory,

Seven major plates carry the continents and ocean basins, Gary Nottis, with the New York State Geological Survey, explained earlier. Due to forces in the earth’s molten interior, the tectonic plates move, at a rate of up to four inches per year. The plates separate or collide along their borders as they move, causing earthquakes and tremors, Nottis said. Most quakes in the United States take place at the edges of tectonic plates.

Ebel explained why earthquakes occur in the Northeastern United States, despite it not being along the border of a tectonic plate.

Since North America is slowly spreading toward the Pacific, the North American plate is being squeezed, resulting in a build-up of tension. The pressure being released is what is causing the earthquakes, said Ebel.

“It’s just like if you were sqeezing a brick in a vise. The brick will eventually break, but you can’t predict when,” Ebel said.

Just as it is hard to say when a brick in a vise would break, it is hard to predict when an earthquake will occur, according to Ebel. The spread of North America toward the Pacific is happening so slowly, over thousands and millions of years, that it is virtually impossible to tell when the pressure will be released, he said.

As for why the earth is shaking more frequently in southern Albany County, as opposed to other areas in the Northeast, Ebel said no one reason can scientifically explain it. The region has not only been active in the past few months; Ebel said there have been earthquakes over the past 25 to 30 years.

“Perhaps there is an active fault, but right now there’s no geologic evidence of that. We are continuing to study the area in hopes that we can find an answer,” said Ebel.